1. Field of the Invention
The present invention relates to the production of an aqueous phosphoric acid solution from elemental phosphorus material.
2. Description of the Prior Art
Phosphoric acid is currently commercially manufactured by either the wet process or the furnace process. In the wet process technique, the phosphoric acid is manufactured by digestion of phosphate rock (apatite forms) with sulfuric acid. The phosphoric acid is then separated from the resulting calcium sulfate slurry by filtration.
In the manufacture of phosphoric acid from elemental phosphorus, white or yellow phosphorus is burned in excess air, the resulting phosphorus pentoxide is then hydrated in a separate step, the heats of combustion and of hydration are removed, and the phosphoric acid mist is collected. The technique of burning the elemental phosphorus in excess air is highly exothermic generating extremely large amounts of heat. John R. Van Wazer, "Phosphorus and its Compounds", Volume II (1961), page 1209, indicates that there have not been successful ways to convert the heat liberated from the exothermic burning of phosphorus to either mechanical or other useful energy primarily because of the extremely corrosive nature of the system involved. Therefore, persons of ordinary skill in the art have generally allowed the heat to escape with a substantial loss of heat energy. Phosphorus furnace plants are rather large and expensive to build since they need special materials to withstand the exothermic and corrosive nature of the various reaction conditions existing therein.
U.S.S.R. Pat. No. 697,401 describes the treatment of phosphorus-containing sludge, while being heated, with an oxygen-containing gas, apparently in the absence of an aqueous covering layer. The treated sludge is then treated in a fluidized bed at elevated temperature to yield a granular product, rather than a solution, having an increased P.sub.2 O.sub.5 content.